According to Freundlich isotherm, the amount of gas adsorbed(x) per unit mass of solid adsorbent (m) is related with pressure(P) at a particular temperature is given by:

x/m = k.P^1/n ( n > 1)

So, log(x/m) = 1/n.logP + logk ……..(equation-I)

So if we plot log(x/m) on y-axis and vs. logP in x-axis, it comes to be a straight line only.

In (i) and (ii) log(x/m) is being plotted against pressure P, which are not possible according to Freundlich adsorption isotherm(equation –I). So both (i) and (ii) are not possible.

According to equation – I, logk is the intercept when log(x/m) is plotted against logP. But in (iv) value of logk is zero. So option (iv) is also not possible.

Therefore, the correct option is (iii), which is in accordance with Freundlich isotherm.